Trump's soft underbelly

Donald Trump is riding a wave of support into Tuesday’s Republican presidential debate, but not in Iowa — a potential roadblock that could halt the businessman’s momentum over the next critical six weeks of this 2016 race.

Nationally, the top-line numbers are striking: Trump is hovering around 40 percent in two new polls conducted entirely after he called for a halt to Muslim immigration, hitting 41 percent in a Monmouth University poll released Monday and 38 percent in an ABC News/Washington Post poll out Tuesday morning.

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And even beneath the surface, the national surveys look good for Trump. The Monmouth poll shows Trump’s favorability rating at a healthy 61 percent, with only 23 percent viewing the real-estate tycoon unfavorably. (Former Florida Gov. Jeb Bush’s favorability rating, for comparison, is 34 percent favorable/47 percent unfavorable.)

In the ABC News/Washington Post poll, Republicans — by a wide margin — say Trump has the best chance to win the election and is the strongest leader.

But it’s a different story in Iowa, with 48 days to go until the Feb. 1 caucuses. The two latest polls — from The Des Moines Register/Bloomberg Politics and Fox News — show Texas Sen. Ted Cruz, not Trump, in first place, though by varying margins. The Des Moines Register/Bloomberg poll, conducted by legendary Iowa pollster J. Ann Selzer, had Cruz ahead of Trump by a 10-percentage-point margin, while the Fox News survey had the candidates closer, with Cruz leading by just 2 points.

Trump is fond of citing a CNN poll released last week showing him with a 13-point lead in Iowa instead — but that poll was conducted Nov. 28-Dec. 6, before the two most recent surveys. And other Iowa polls from early December more closely resemble the Des Moines Register and Fox polls, including surveys from Monmouth and Quinnipiac universities that show a tight race between Cruz and Trump.

So why the dissonance between Republicans in Iowa and the rest of the country? In part, it’s because Iowa Republicans have seen more candidates than potential primary voters or caucus-goers across the country. They know more about Cruz, who is banking on a strong performance in the evangelical-heavy caucuses to propel his campaign.

But, in an interview last month with POLITICO, Selzer, the Des Moines Register pollster, cautioned that, despite the increased exposure to the candidates, the state of play in Iowa is still fluid.

“It changes up until the very last day,” Selzer said. “And that’s kind of the Iowa assignment. Which is: No state is going to look at more candidates than Iowa. And our job is to kind of keep an open mind. You shouldn’t be surprised that people are unwilling to be locked down. In fact, walking into caucus, they’re going to hear their neighbors, some people are going to talk about these candidates before they ever cast a vote. It’s designed for people to change their mind.”

Perhaps the most significant reason for the differing poll numbers in Iowa and across the country is methodological, however. Since each state sets its own rules about who may cast ballots in the GOP nominating contest — not to mention Colorado, which won’t have presidential preference voting at all — national pollsters simply include all registered voters who say they are either Republicans or independents who lean toward the Republican Party or say they’ll vote in the GOP primary, regardless of whether their state allows independents to take part in the primary or caucus.

A number of Republicans haveargued for the past six months that this one-size-fits-all voter screen is too broad and that it’s creating an artificial bubble for the front-runner because Trump’s supporters haven’t been as likely to vote in past nominating contests.

Yet, despite Iowa’s high profile, very few voters actually participate: The number of votes cast in the 2012 GOP caucuses was less than one-fifth the number of registered Republican voters on the rolls. That forces pollsters to construct a screen designed to weed out those Republicans who are unlikely to travel to a caucus site on a cold, February night. Even those polls that use the loosest possible screen — asking voters if they intend to participate in a caucus — are more restricting than the national surveys of all self-identified Republicans.

Trump’s lead in national polls at this point of the campaign — even wide advantages like the 27-point ead he posted in the Monmouth poll, or the 23-point bulge in the ABC News/Washington Post poll — is hardly predictive of a glide path to the nomination. And even if he maintains that edge going into Iowa, there’s evidence that the caucuses can scramble the race — even if the winner of the caucuses doesn’t become the eventual nominee.

Former House Speaker Newt Gingrich entered the 2012 caucuses with a lead in the national polls, though former Massachusetts Gov. Mitt Romney was close on his heels. Former Sen. Rick Santorum (R-Pa.) would overtake Romney for a time after his narrow victory in the caucuses, but Gingrich faded quickly after his disappointing fourth-place finish.

Former Arkansas Gov. Mike Huckabee had the lead in national polls going into the 2008 caucuses, which he then won over Romney. But Sen. John McCain (R-Ariz.) won New Hampshire over Romney and Huckabee and cruised to the nomination.

Quinnipiac poll assistant director Peter Brown — in an interview earlier this month with POLITICO — pointed to neither Gingrich nor Huckabee, but to 2004 Democratic candidate Howard Dean. The former Vermont governor was leading in national surveys going into the Jan. 19 caucuses. But his support collapsed after a third-place finish in Iowa, and the Iowa victor, then-Sen. John Kerry (D-Mass.) had a stranglehold on the race within two weeks.

“[Dean] was leading, leading, leading until they actually started voting,” said Brown. “There a lot of people who don’t like Trump who like that scenario. It has happened — but it doesn’t mean it’s going to happen this time.”